Monitoring focus - The UK Butterfly Monitoring Scheme

JNCC works with partners to run a number of long-term biodiversity monitoring schemes in the UK. In this edition of Nature News we look at the UK Butterfly Monitoring Scheme (UKBMS). The scheme benefits from the commitment of thousands of skilled volunteer recorders – with over 3000 recorders monitoring a record 2873 sites in 2018.

Peacock butterfly © Natural England/Allan Drewitt

Since 1976, the UKBMS has monitored changes in the abundance of butterflies throughout the UK. The scheme, run by Butterfly Conservation (BC), the Centre for Ecology and Hydrology (CEH), JNCC and the British Trust for Ornithology (BTO), currently has three components. The original recorder-selected ‘Pollard walk’ transects are monitored every week throughout the summer. ‘Wider Countryside Butterfly Survey’ survey lines, which follow a prescribed route and are sited in random 1km squares, are walked at least twice between July and August. A small number of targeted species surveys also take place, including standardised counts of specific butterfly species, egg, larval or adult forms.

The latest results of the UKBMS (released as Official Statistics on 29 March at http://www.ukbms.org/official_statistics) show that last year’s hot, sunny summer benefited many species, with over two thirds showing an increase in 2018 compared with 2017. However, abundance levels were only slightly above average for the series as a whole. Over a third of butterfly species in the UK are showing a significant long-term decline in abundance, approximately twice as many as those showing a significant long-term increase. Whilst weather conditions can create noticeable fluctuations in butterfly populations from one year to the next, long-term trends showing a decline in abundance are attributable to changes in the extent, condition and fragmentation of habitats caused by the intensification of farming, forestry practices, urban development, pollution and climate change.

The UKBMS is highly valued as a key evidence source by the UK’s NGOs, country conservation and research bodies. Results from the scheme feed into the UK Biodiversity Indicator – Insects of the wider countryside. UKBMS results also feed into England and Scotland indicators, and may feed into indicators currently under development in Wales. The data also contribute to the European Grassland Butterflies indicator. Sadly, indicators are reflecting the long-term declines in abundance, particularly so for habitat specialist species. However, landscape-scale conservation efforts can play an important role in improving the fortunes of declining butterfly species, and there have been some success stories. Woodland coppicing, to create more open areas that can support butterflyfood plants, has been successfully carried out for the Heath Fritillary. Management of unimproved grassland has benefited the endangered Large Blue, for which 2018 was the best year on record with numbers having almost tripled in the past ten years. The Large Blue is protected under the Habitats Directive, and UKBMS data have been valuable in helping the UK meet its reporting obligations, contributing to the wider understanding of this species at a European level.

Ongoing monitoring through the UKBMS is important to help us better understand the environment, identify where there are problems, and thus provide a stimulus for conservation action.

Butterfly populations are good indicators of environmental change due to their rapid and sensitive responses to subtle habitat or climatic changes, and as representatives for the diversity and responses of other wildlife.

Country level results

As the UKBMS sample size has increased it has become possible to analyse trends for the different countries in the UK. In 2018 there were sufficient data to produce trends for 55 species in England, 13 species in Northern Ireland, 25 species in Scotland, and 33 species in Wales. Trends were similar to overall UK trends.

The following species fared particularly well in each country in 2018.

England

Large Blue, Black Hairstreak, Dingy Skipper, Green-veined White, High Brown Fritillary, Purple Hairstreak

Wales

Brimstone, Grayling, Painted Lady, Small Tortoiseshell

Scotland

Comma, Grayling, Large White, Ringlet

Northern Ireland

Marsh Fritillary, Peacock

Contact:

Anna Robinson Monitoring Ecologist anna.robinson@jncc.gov.uk